focus rectifier sub.

[bgadow]

I fought a Zenith with gradually diminishing focus and nothing seemed to help, until I replaced the horiz output tube.

[DaveWM]

its not gradual, it will be fine, then kinda pop in and out of focus, while I am watching it. Just started this. That's why I was wondering what is the failure mode of a focus stack, do they just go bad or is there a period where they get intermittent then with longer and longer "bad" times.

[DaveWM]

I have a test procedure, used it on a known bad vs a NOS that worked. I use my eye tube tester as a B+ and measure the current thru it (or was it the voltage, does not matter since the eye tube is a load). IIRC the bad one was much lower in voltage/current AND jumpy..